JP2003138168A - Ink set for ink jet recording and ink jet printing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink set for ink jet recording which achieves high image quality (prevention of bleeding for a color image) and high-speed printing with respect to ink jet recording, particularly color ink jet recording. Provided is an ink jet printing method using the method. SOLUTION: An ink set for ink jet recording comprising both a recording ink containing at least a colorant and an ultrafine particle pigment having a volume average particle diameter of 60 nm or less and a printability improving liquid for improving printability in an ink jet printer. And an inkjet printing method using the same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet recording ink set and a printing method for forming an image using an inkjet recording system.

[0002]

2. Description of the Related Art Up to now, various methods have been proposed for high image quality and high speed technology in image formation by an ink jet recording system. Among them, the ink jet recording method of printing two liquids of an ink composition and a printability improving liquid different from the ink composition is practically used as a method for obtaining a high-quality color image having a high image density on plain paper and no color bleeding. It has become a reality. However, in the image formation by the ink jet recording method, it is the current situation that higher image quality and higher speed are desired. On the other hand, in the development of coloring materials for inks used in office and personal inkjet printers, in addition to dye-based coloring materials that have been mainstream for many years, pigment-based coloring materials have been actively developed in recent years. In particular, future development is strongly desired due to the high weather resistance [water resistance, light resistance, gas resistance (ozone resistance), etc.] which is a characteristic of pigment-based coloring materials.

In recent years, development of a manufacturing method for making fine particles of a chromatic organic pigment has progressed, and so-called ultrafine particle color (chromatic color) organic pigments which can be used for ink jet recording have appeared. The ultrafine particle color organic pigment has an effect of improving print quality such as coloring and transparency on a recording medium, which is inferior to conventional color pigment inks compared with dye inks.

On the other hand, a number of two-component ink jet recording methods using a pigment ink and a liquid containing a reactive agent having reactivity with the ink as a different printing property improving liquid have been reported so far. ing. However, none of the conventional techniques is at a satisfactory level in terms of achieving both high-speed fixability and high image density for high-quality image recording while realizing high-speed printing. In the conventional two-component ink jet recording method, no one paid attention to the average particle size of the pigment ink and its particle size distribution. In the present invention, by using a pigment ink containing an ultrafine particle pigment having a volume average particle diameter of 60 nm or less, high-speed fixability and high image quality in plain paper recording, which cannot be achieved by the conventional two-component ink jet recording method, are achieved. It became possible to achieve both.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to achieve high image quality and high printing speed in ink jet recording, particularly color ink jet recording, and more specifically, To achieve the following points. (1) A sufficient image density is obtained and the solid image has high uniformity. (2) The character quality is good while having a good fixing property. (3) Prevent bleeding. (4) Color reproducibility is good and a high-definition image can be obtained. (5) The recorded image has good weather resistance (water resistance, light resistance, gas resistance). (6) The recorded image has good scratch resistance and line marker resistance. In addition, in addition to the above, the following points are achieved particularly in plain paper color recording in the ink jet system. (7) High-speed fixing property, high image density, and bleedlessness are all satisfied.

[0006]

The above object can be achieved by the present invention described below. That is, the present invention is characterized in that it comprises at least a recording ink containing an ultrafine particle pigment having a volume average particle diameter of 60 nm or less as a colorant, and a printability improving liquid for improving printability in an inkjet printer. And an ink set for inkjet recording. In a particularly preferred form of the ink set, the ultrafine particle pigment used as the colorant has a volume average particle diameter of 60 nm or less and a cumulative 90% particle diameter of the volume particle diameter distribution of 100 nm or less.

In another preferable form of the ink set, the ultrafine particle pigment is a chromatic organic pigment. Further, it reacts when the recording ink and the printability improving liquid come into contact with each other. The ultrafine pigment is a chromatic organic pigment having a functional group dispersible in an aqueous medium on its surface, and the functional group dispersible in the aqueous medium is an anionic group. It is a thing. Further, in this case, the printing property improving liquid may include at least a cationic compound or at least a polyvalent metal salt.

Another preferred form of the ink set is a chromatic organic pigment in which the ultrafine particle pigment is dispersed by a dispersant. Further, the dispersant is a dispersant having an anionic property, and in this case, the printability improving liquid further contains at least a cationic compound. Further, in this case, the form in which the printability improving liquid contains at least a polyvalent metal salt can be mentioned.

As another preferable form of the ink set, the printability improving liquid contains at least a water-soluble resin component, and the printability improving liquid is dispersed or dissolved in at least an aqueous medium. And a resin component having both a hydrophilic part and a hydrophobic part. Further, the recording ink is composed of a combination of at least four inks of black, cyan, magenta, and yellow, and among these inks, the chromatic ink contains at least an ultrafine particle pigment as a colorant.

Another embodiment of the present invention is a method for forming a colored portion on a recording medium using any of the above ink sets, which comprises (i) applying the recording ink to the recording medium, And (ii) a step of applying the printability improving liquid to the recording medium, wherein the recording ink and the printability improving liquid are applied so as to be in liquid contact with each other on the surface of the recording medium. A method for printing a colored portion on a recording medium that is a feature.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below with reference to preferred embodiments. As a result of intensive studies to solve the above-mentioned problems of the prior art, the present inventors have used an ultrafine particle pigment as a colorant constituting a pigment ink, and perform printing using a printability improving liquid together with it. Finds that the compatibility of high-speed fixability and high image density can be achieved at a level never before achieved by
The present invention has been completed. In particular, if an ultrafine particle chromatic color organic pigment is used as the ultrafine particle pigment, high-speed printing can be realized and high-quality color image recording can be performed.

Hereinafter, the printability improving liquid for improving the printability used in the ink jet printing method of the present invention will be described. The printability improving liquid in the present invention has a function of improving printability in an inkjet printer, and specifically has the following functions. 1. A function to improve the fixability of recording ink in plain paper recording. 2. A function that reduces bleeding between different colors of different colors in a plain paper record. 3. A function to improve the image density and color reproduction range of recorded images in plain paper recording. 4. Function to improve scratch resistance and line marker resistance of recorded images. The printability improving liquid used in the present invention has the above-mentioned functions 1. ~ 4. May be used to achieve at least one of ~ 4. May be provided at the same time.

As the printability improving liquid in the present invention, the above-mentioned functions 1. ~ 4. In order to achieve the above, specifically, those containing the following components are used. (A) A printability improving liquid containing a component capable of reacting when brought into contact with a recording ink to destroy the dispersed state of the colorant component in the recording ink. (B) A printability improving liquid containing at least a water-soluble resin or a resin component having both a hydrophilic part and a hydrophobic part which are dispersed or dissolved in an aqueous medium.

First, a printability improving liquid satisfying the above constitution (a) [hereinafter referred to as printability improving liquid (a)] will be described. The printability improving liquid (a) has the function 1. ~ 3. At the same time,
It is characterized in that it contains a component (hereinafter, abbreviated as a reactive agent) capable of reacting when brought into contact with the recording ink to destroy the dispersed state of the colorant component in the recording ink.

The reactive agent in the printability-improving liquid (a) is not limited as long as it can destroy the dispersed state of the colorant component in the recording ink by contact with the ink, but the following are preferred. There are two types. I) A compound having a polarity opposite to that of the recording ink. B) A compound that changes the pH of the ink from a stable region of the colorant in the ink to an unstable region by contact with the recording ink.

The printability improving liquid containing the above component (1) will be described. As the recording ink used for ink jet recording, a preferable one has an anionic property as described later, and in this case, the printability improving liquid is constituted by containing a cationic component having a polarity opposite to that of the printing property improving liquid. Examples of the cationic component used in that case include high molecular compounds having at least a cationic group, low molecular weight cationic compounds such as oligomers and surfactants, and polyvalent metal salts.

Examples of the cationic polymer substance include polyallylamine hydrochloride, polyaminesulfone hydrochloride, polyvinylamine hydrochloride, chitosan acetate and the like. Of course, the compounds are not limited to these compounds, and are not limited to the hydrochloride type and acetate type compounds. In addition to the above-listed compounds, the following nonionic polymer substances may be used, in which a part of the nonionic polymer is cationized. Specific examples thereof include a copolymer of vinylpyrrolidone and a quaternary salt of aminoalkyl alkylate and a copolymer of a quaternary salt of acrylic amide and aminomethyl acrylic amide. Of course,
Needless to say, it is not limited to these compounds.
Further, the polymer substances and the cationic polymer substances listed above are satisfactory if they are water-soluble.
It may be a dispersion such as latex or emulsion.

Specific examples of the low molecular weight cationic compound that can be used in the present invention are listed below. However, it goes without saying that the present invention is not necessarily limited to the low molecular weight cationic compounds exemplified below. As the low molecular weight cationic compound, first, a primary, secondary or tertiary amine salt type low molecular weight cationic compound can be used. Specifically, laurylamine,
Hydrochloric acid salts of coconut amine, stearyl amine, rosin amine, etc., acetates, etc. may be mentioned. Further, a quaternary ammonium salt type low molecular weight cationic compound can be used.
Specific examples include lauryl trimethyl ammonium chloride, lauryl dimethyl benzyl ammonium chloride, benzyl tributyl ammonium chloride, benzalkonium chloride and the like. Further, a pyridinium salt type low molecular weight cationic compound can be used.
Specific examples include cetylpyridinium chloride and cetylpyridinium bromide. An imidazoline type low molecular weight cationic compound can be used, and specific examples thereof include 2-heptadecenyl-hydroxyethyl imidazoline. Further, a low molecular weight cationic compound such as an ethylene oxide adduct of a higher alkylamine can be used, and specific examples thereof include dihydroxyethylstearylamine.

Further, in the present invention, as the low molecular weight cationic compound, an amphoteric surfactant having a cationic property in a certain pH range can be used. Examples thereof include amino acid type amphoteric surfactants, R-NH-CH.
Examples thereof include _2- CH ₂ —COOH type compounds and betaine type compounds. More specifically, in addition to carboxylate type amphoteric surfactants such as stearyl dimethyl betaine and lauryl dihydroxyethyl betaine, sulfate ester type compounds. , Amphoteric surfactants such as sulfonic acid type and phosphoric acid ester type can be used. Of course, when these amphoteric surfactants are used, the pH of the printability improving liquid is adjusted so that the pH is below their isoelectric point, or when mixed with a recording ink on a recording medium, It is necessary to adjust the pH of the mixed solution to a pH below their isoelectric point, or to take either method.

Furthermore, examples of the low molecular weight cationic compound that can be used in the present invention include the following polyvalent metal salts. Representative preferred materials include, but are not limited to, salt solutions containing divalent and trivalent metal cations as listed below. That is, the divalent metal cations include Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Zn ²⁺ , and B.
^{Examples of} trivalent metal cations such as a ²⁺ include Al ³⁺ , Y ³⁺ ,
Fe ^{3+ and the} like can be mentioned. In addition, examples of preferable anions that bond with these cations include nitrate ions and acetate ions. However, the present invention is not limited to this.

Next, the printability improving liquid containing the above-mentioned component) will be described. In this case, the printability improving liquid contacts the recording ink
It is characterized in that H is changed from the stable region of the colorant in the ink to the unstable region. As described above, the recording ink used in the present invention is preferably an anionic ink. Therefore, as the material having the above-mentioned configuration in this case, for example, an alkali-soluble resin is used as a dispersant for the ultrafine particle pigment. The alkali-soluble resin has dispersion stability in a liquid having an alkaline to neutral pH, but the resin becomes insoluble in a liquid having an acidic or weakly acidic pH, and thus is contained as a colorant in the recording ink. It is possible to cause dispersion destruction of the ultrafine particle pigment.

Therefore, at least an acidic component is contained in the printability improving liquid having the above-mentioned component (a) used when the recording ink contains an alkali-soluble resin as a dispersant for the ultrafine particle pigment. As the acidic component used in that case, all inorganic acids and organic acids can be applied, and examples thereof include acetic acid, nitric acid, hydrochloric acid, lactic acid, succinic acid, gluconic acid, glycolic acid and the like. To be However, the present invention is not limited to these.

Functions 1 to 3 described above by the printability improving liquid (a) having the specific constitution as described above.
The effect that is achieved is expected to be as follows.
At the time of image formation, on the recording paper or where it has penetrated,
When the printability-improving liquid and the recording ink are mixed, the reactive agent in the printability-improving liquid reacts with the ultrafine particle pigment as a colorant contained in the recording ink to cause momentary agglomeration, resulting in a pigment component in the ink. And the solvent component are separated (hereinafter, this phenomenon is referred to as solid-liquid separation), and only the solvent component penetrates into the recording paper, while the pigment component, which is the coloring material, efficiently remains on the paper surface. As a result, the image density and color reproduction range of the recorded image are improved, and blurring of different color boundaries between different colors of the recorded image does not occur. Further, the fixability of the ink can also be improved by adding a surfactant having a high permeability to paper or a solvent component in the printability improving liquid.

Next, the printability containing at least the water-soluble resin having the above-mentioned constitution (b) or the resin component having both the hydrophilic part and the hydrophobic part which are dispersed or dissolved in the aqueous medium. The improvement liquid will be described. The printability improving liquid having the structure of (b) [hereinafter referred to as the printability improving liquid (b)] is used to satisfy all the four functions listed above. As the resin to be contained in the printability improving liquid (b), for example, a resin obtained by polymerization of a known vinyl monomer which is usually used as a pigment dispersant can be mentioned. More preferably, a resin having a cationic property is used. In this case, the printability-improving liquid (b) is also a printability-improving liquid (a) at the same time, and it is more preferable because it has both functions.

The resin having a cationic property that can be used in the present invention is obtained by using a cationic monomer which forms at least a part of the following. That is,
For example, salts of tertiary amine monomers and quaternized compounds thereof can be mentioned. Specific compounds include, for example, the compounds listed below. N, N-dimethylaminoethyl methacrylate _{[CH 2 = C (CH 3)} -COO-C 2 H 4 N (CH 3) 2 ], N, N-dimethylaminoethyl acrylate _{[CH 2 = CH-COO-C} 2 H ₄ N (CH _{3) 2],} N, N-dimethylaminopropyl methacrylate _{[CH 2 = C (CH 3)} -COO-C 3 H 6 N (CH 3) 2 ], N, N-dimethylaminopropyl acrylate _{[CH 2 = CH-COO-C} 3 H 6 N (CH 3) 2 ], N, N-dimethylacrylamide _{[CH 2 = CH-CON (CH} 3) 2 ], N, N-dimethyl methacrylamide [CH _{2 = C (CH 3) -CON (} CH 3) 2 ], N, N-dimethylaminoethyl acrylamide _{[CH 2 = CH-CONHC 2 H} 4 N (CH 3) 2 ], N, N-dimethylaminoethyl methacrylamide _{[CH 2 = C (CH 3)} - _{ONHC 2 H 4 N (CH 3} ) 2 ], N, N-dimethylaminopropyl acrylamide _{[CH 2 = CH-CONH-C} 3 H 6 N (CH 3) 2 ], N, N-dimethylaminopropyl methacrylamide [ _{CH 2 = C (CH 3)} -CONH-C 3 H 6 N (CH 3) 2 ],

In the case of a tertiary amine, examples of the compound for forming a salt include hydrochloric acid, sulfuric acid, acetic acid and the like, and examples of the compound used for the quaternization include methyl chloride, dimethylsulfate and benzyl. Examples thereof include chloride and epichlorohydrin. Among these, methyl chloride, dimethylsulfate and the like are preferable for preparing the resin used in the above. The salt of the tertiary amine or the quaternary ammonium compound as described above behaves as a cation in water, but the acid is a stable dissolution region under neutralized conditions.

Other monomers which can be used in the present invention to form the cationic resin include, for example, 2-hydroxyethyl methacrylate, acrylic acid having a hydroxy group such as acrylic acid ester having a long ethylene oxide chain as a side chain. Hydrophobic monomers such as esters and styrene-based monomers, and acrylamides, vinyl ethers, vinylpyrrolidones, vinylpyridines capable of forming water-soluble monomers that are soluble in water near pH 7;
Examples thereof include vinyl oxazolines. As the hydrophobic monomer, a hydrophobic monomer such as styrene, a styrene derivative, vinylnaphthalene, a vinylnaphthalene derivative, an alkyl ester of (meth) acrylic acid, or acrylonitrile is used.

3. The function described above by the printability improving liquid (b). The effect that is achieved is expected to be as follows. Generally, in a resin-dispersed pigment ink as a recording ink, the resin as the dispersant has a scratch resistance of a recorded image,
Although it is a well-known fact that the line marker resistance is improved, the amount of resin added as the dispersant has an upper limit in consideration of inkjet dischargeability. Therefore, as the printability-improving liquid, a water-soluble resin as described above or a resin component having both a hydrophilic part and a hydrophobic part in a dispersed or dissolved state in an aqueous medium is further added, By forming a stronger film on the recording medium, the scratch resistance and line marker resistance of the recorded image can be further perfected. When a self-dispersion type fine particle pigment that does not use a dispersant is used as the colorant to be contained in the recording ink, the scratch resistance and the line marker resistance are not particularly good. By using the printability improving liquid (b), it becomes possible to form a recorded image having excellent scratch resistance and line marker resistance.

When the resin contained in the printability improving liquid (b) is, for example, a resin having a cationic property, of course, the function exhibited by the printability improving liquid (a) described above is exerted. In addition, when the component contained in the printability improving liquid (a) is a polymer component (resin), it may also have the function exhibited by the printability improving liquid (b). . Furthermore, it goes without saying that the printability-improving liquid used in the present invention may be a printability-improving liquid that simultaneously satisfies both the configurations (a) and (b) described above.

Next, the recording ink used in the present invention together with the above printability improving liquid will be described. The recording ink used in the present invention contains an ultrafine particle pigment as a colorant as at least an essential component. In the present invention, the ultrafine particle pigment is defined as having a volume average particle diameter of 60 nm or less measured by a dynamic light scattering method. A more preferable ultrafine particle pigment has a volume average particle diameter of 60 nm or less measured by a dynamic light scattering method,
In addition, fine particles having a cumulative 90% particle diameter of the volume particle diameter distribution of 100 nm or less are included. The ultrafine particle pigment that can be used in the present invention may be either an inorganic pigment or an organic pigment.

The measuring method of the average particle diameter and the particle diameter distribution in the present invention is as follows: Microtrac UPA15
0 (manufactured by Nikkiso Co., Ltd.) is used. As the measurement conditions,
The sample solution is diluted with ion-exchanged water, dispersed in an ultrasonic cleaner, and measured under the condition that the sample concentration index is in the range of 0.01 to 0.1.

As the inorganic pigment, for example, those containing carbon as a main component such as carbon black can be used. Organic pigments include cyan, magenta, yellow,
Conventionally known organic pigments having chromatic colors such as red, green and blue can be used without any distinction. A plurality of these chromatic organic pigments may be mixed and used. Typical examples of organic pigments include, for example, quinacridone pigments, quinacridone quinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, anthanthrone pigments, indanthrone pigments, flavanthrone. Pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments,
Examples thereof include thioindigo pigments, benzimidazolone pigments, isoindolinone pigments, azomethine pigments and azo pigments.

The method for producing the ultrafine particle pigment is not particularly limited as long as it is a production method capable of obtaining ultrafine particles having a volume average particle diameter of 60 nm or less, and an existing production method is used. As the disperser used in this case, any disperser generally used can be used. Specifically, for example, a ball mill, a roll mill, a dispersing machine such as a sand mill, and the like, a high speed sand mill is preferable among these, for example, a super mill, a sand grinder, a bead mill, an agitator mill, a grain mill, a dyno mill, a pearl mill, Cobol mill (both are trade names)
Etc. can be preferably used.

As a method for obtaining a pigment dispersion or ink having a desired particle size distribution, the following method can be used. For example, by reducing the size of the crushing media used in the disperser, increasing the packing rate of the crushing media, lengthening the crushing treatment time, slowing the crushing speed, or using a filter or a centrifugal separator after crushing. A method such as classification can be used. Of course, these methods may be combined appropriately.

As a method for obtaining ultrafine particles, a method called a vapor phase method may be used. The gas phase method is a step of generating a plasma of a gas containing at least a reactive gas, a step of evaporating a raw material and generating ultrafine particles by passing through the gas, and a plasma of a gas containing the reactive gas. It is a method comprising a step of modifying ultrafine particles by passing through the inside.

The ultrafine particle pigment used in the present invention may be a self-dispersion type pigment having its fine particle surface modified, or a resin dispersion type pigment dispersed with a water-soluble resin or the like. In either case, preferably,
It preferably has an anionic group.

Examples of the anionic self-dispersion pigment include the following. -COO (M _2), - SO
_{3 (M 2), - PO} 3 H (M 2) and -PO ₃ (M _{2) 2} (where
In the above formula, M ₂ represents a hydrogen atom, an alkali metal, ammonium or organic ammonium. )

In the case of the resin-dispersed pigment, the dispersant itself may contain an anionic group, or if the dispersant does not have an ionic group, the ink may contain other anionic compound. Good. Of course, the dispersant itself may contain an anionic group, and may further contain an anionic compound.

As the dispersant for the pigment used, any water-soluble resin can be used, but the weight average molecular weight is preferably in the range of 1,000 to 30,000. Furthermore, it is preferably in the range of 3,000 to 15,000. Specifically, styrene, styrene derivatives, vinylnaphthalene, vinylnaphthalene derivatives, α,
Hydrophobic monomer such as aliphatic alcohol ester of β-ethylenically unsaturated carboxylic acid, or acrylic acid, acrylic acid derivative, maleic acid, maleic acid derivative, itaconic acid, itaconic acid derivative, fumaric acid, fumaric acid derivative Examples thereof include block copolymers, graft copolymers, random copolymers composed of two or more monomers selected from the above, and salts thereof. These resins are alkali-soluble type resins that are soluble in an aqueous solution in which a base is dissolved. Further, a homopolymer composed of a hydrophilic monomer or a salt thereof may be used. It is also possible to use water-soluble resins such as polyvinyl alcohol, carboxymethyl cellulose, and naphthalene sulfonic acid formaldehyde condensate.

The recording ink used in the present invention is, in addition to the above-mentioned ultrafine particle pigment and the pigment dispersant used as necessary, an aqueous medium such as water or a water-soluble organic solvent for dispersing the pigment, And other additives such as viscosity modifiers,
A pH adjuster, an antiseptic, a surfactant, an antioxidant, an anti-curl agent and the like are contained as necessary.

[0041]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited to the following examples unless it exceeds the gist. In the text, "part" or "%" is based on mass unless otherwise specified.

In carrying out the invention, first, recording ink sets 1 to 3 in which the following four recording inks were combined and printability improving liquids 1 to 4 to be used with them were prepared. Recording ink set 1 (Y, M, C, Bk are ultrafine resin dispersion pigments) Recording ink set 2 (Y, M, C are ultrafine resin dispersion pigments, Bk is ultrafine particles Of the resin dispersion type pigment larger than the definition range of recording ink set 3 (Y, M, and C are ultrafine particle self-dispersion type pigments, and Bk is a resin dispersion type pigment having a particle size larger than the definition range of ultrafine particles. ) ・ Printability improving liquid 1 (Bleeding resistance and fixing property improving liquid (using organic low molecular cations)) ・ Printing property improving liquid 2 (bleeding resistance and fixing property improving liquid (using polyvalent metal salts)) ・Printability improving liquid 3 (rubbing resistance improving liquid) -Printability improving liquid 4 (bleeding resistance, fixing property, rubbing resistance improving liquid)

(Preparation of Recording Ink Set 1) <Preparation of Yellow Ink 1> First, a styrene-acrylic acid copolymer (Joncryl 678, manufactured by Johnson Polymer Co.) and a predetermined amount necessary for neutralizing the same. Potassium hydroxide and water were mixed, and these were stirred and mixed while keeping the temperature at about 60 ° C. to prepare a 10% styrene-acrylic acid copolymer aqueous solution. Then, the styrene-acrylic acid copolymer prepared as described above was used as a dispersant to prepare the following yellow pigment dispersion.

[0044] 30 parts of 10% styrene-acrylic acid copolymer aqueous solution ・ Pigment Yellow 74 6 parts ・ Glycerin 20 parts ・ Diethylene glycol 20 parts ・ Triethylene glycol 10 parts ・ Ion-exchanged water 14 parts

These materials were charged into a batch type vertical sand mill, glass beads having a diameter of 200 μm were filled as a medium, and while being cooled with water, a grinding medium speed of 9,000 rpm was used for 5 times.
Dispersion processing was performed over time. The yellow pigment dispersion was centrifuged (10,000 rpm, 30 minutes), and then the whole was diluted twice with water to form an ink. Further, this ink was subjected to dispersion treatment for 5 hours in the above high speed mill.
After that, by performing centrifugal separation treatment (10,000 rpm, 30 minutes) to remove coarse particles, an ink was prepared so as to have a predetermined composition. Finally, 1% by mass of acetylenol EH (manufactured by Kawaken Chemicals Co., Ltd.) was added to this ink, the mixture was stirred and mixed, and then filtered with a 1 μm membrane filter to obtain yellow ink 1.

The volume average particle size and volume particle size distribution of the yellow ink 1 thus obtained were measured. Microtrac UPA150 (manufactured by Nikkiso Co., Ltd.) was used as the device. As the measurement conditions, the yellow ink 1 was diluted with ion-exchanged water and then dispersed with an ultrasonic cleaner, and the sample concentration index was measured at 0.04. as a result,
The volume average particle diameter of the yellow ink 1 is 13 nm,
The cumulative 90% particle size of the volume particle size distribution was 14 nm.

<Preparation of Magenta Ink 1> Pigment Yellow 74 (6 parts) and ion-exchanged water (14 parts) in Yellow Ink 1 were changed to Pigment Red 122 (8 parts) and ion-exchanged water (12 parts), respectively. Except that, magenta ink 1 was prepared under the same conditions and operations as those of yellow ink 1. The volume average particle size and volume particle size distribution of the magenta ink 1 thus obtained were measured in the same manner as the yellow ink 1. As a result, the volume average particle diameter of magenta ink 1 was 46 nm, and the cumulative 90% particle diameter of the volume particle diameter distribution was 85 nm.

<Preparation of Cyan Ink 1> Cyan is exactly the same as the preparation of Yellow Ink 1 except that Pigment Yellow 74 (6 parts) in Yellow Ink 1 is changed to Pigment Blue 15: 3 (6 parts). Ink 1 was prepared. The volume average particle diameter and volume particle diameter distribution of the cyan ink 1 thus obtained were measured in the same manner as the yellow ink 1. As a result, the volume average particle diameter of cyan ink 1 was 50 nm, and the cumulative 90% particle diameter of the volume particle diameter distribution was 69 nm.

<Production of Black Ink 1> Pigment Yellow 74 (6 parts) and ion-exchanged water (14 parts) in Yellow Ink 1 were carbon black (MCF88: manufactured by Mitsubishi Chemical Corporation) (10 parts) and ion-exchanged, respectively. Black Ink 1 was prepared under exactly the same conditions as in Yellow Ink 1 except that water (10 parts) was used.
The volume average particle size and volume particle size distribution of the black ink 1 thus obtained were measured in the same manner as the yellow ink 1. As a result, the volume average particle diameter of the black ink 1 is 4
8 nm, cumulative 90% particle diameter of volume particle size distribution is 90 n
It was m.

(Preparation of Recording Ink Set 2) The yellow ink 2, the magenta ink 2, and the cyan ink 2 were the same as the yellow ink 1, the magenta ink 1, and the cyan ink 1, respectively. <Black ink 2
Preparation> The same material as that of Black Ink 1 was charged into a batch type vertical sand mill, glass beads with a diameter of 500 μm were filled as a medium, and while being water cooled, a grinding medium speed of 5,00
Dispersion treatment was performed at 0 rpm for 5 hours. This black pigment dispersion was centrifuged (10,000 rpm, 3
After 0 minutes), the whole was diluted twice with water to form an ink. Further, this ink is subjected to a centrifugal separation treatment (10,000 r
pm, 30 minutes) to remove coarse particles, and then the ink was adjusted to have a predetermined composition. Finally, 1% by weight of acetylenol EH (manufactured by Kawaken Chemicals Co., Ltd.) was added to this ink, and the mixture was stirred and mixed, and then 1 μm
A black ink 2 was obtained by filtering with a membrane filter of.

(Preparation of Recording Ink Set 3) <Preparation of Yellow Ink 3> Pigment Yellow 128 was used as a raw material for the yellow ultrafine particle pigment, and an anion self-dispersion type whose surface was modified with a carboxyl group by a gas phase method. A yellow ultrafine pigment was obtained. The average particle size of the obtained ultrafine particle pigment was 30 nm. Using this ultrafine particle pigment, Yellow Ink 3 was prepared by the following method.

・ Yellow ultrafine pigment 5 parts ・ Glycerin 7 parts ・ Ethylene glycol 7 parts ・ Trimethylolpropane 7 parts ・ Isopropyl alcohol 2 parts ・ Acetylenol EH 1.0 part ・ Ion-exchanged water 71 parts Sufficiently mixing and stirring the above components In addition, the pore size is 1μ
m membrane filter (trade name: Fluoropore Filter, manufactured by Sumitomo Electric Co., Ltd.) under pressure to obtain a yellow ink 3 of a recording ink set 3.

<Preparation of Magenta Ink 3> Anion self-dispersion magenta ultrafine pigment was obtained by the same preparation method as in Yellow Ink 1 except that Pigment Red 122 was used as the raw material for the magenta ultrafine particle pigment. The average particle size of the obtained ultrafine particle pigment was 35 nm. A magenta ink 3 constituting the recording ink set 3 was obtained by the same method as that for producing the yellow ink 3 using this ultrafine particle pigment.

<Preparation of Cyan Ink 3> Anion self-dispersion type cyan ultrafine particle pigment was obtained by the same preparation method as that of Yellow Ink 3 except that Pigment Blue 15: 3 was used as a raw material for the cyan ultrafine particle pigment. It was
The average particle size of the obtained ultrafine particle pigment was 40 nm. Cyan ink 3 constituting recording ink set 3 was obtained by the same method as that for producing yellow ink 3 using this ultrafine particle pigment.

The same black ink 2 as the black ink 2 was used.

<Preparation of printability improving liquid 1> G-50 (benzalkonium chloride: trade name, manufactured by Sanyo Kasei) 5 parts Glycerin 7 parts Ethylene glycol 7 parts Ion-exchanged water 81 parts Mix the above components After dissolution, the solution was filtered under pressure with a membrane filter having a pore size of 1 μm to obtain a printability improving liquid 1.

<Preparation of printing property improving liquid 2> 4 parts of calcium nitrate, 7 parts of glycerin, 7 parts of ethylene glycol, 1 part of acetylenol EH (manufactured by Kawaken Chemicals Co., Ltd.), 81 parts of deionized water. Furthermore, pressure filtration was performed with a membrane filter having a pore size of 1 μm to obtain a printability improving liquid 2.

<Preparation of printability improving liquid 3> Styrene-N, N-dimethylaminoethylmethacrylate copolymer (molecular weight 20,000) 2 parts Glycerin 5 parts Diethylene glycol 5 parts Acetylenol EH 1.5 parts Ion Exchanged water 86.5 parts The above components were mixed and dissolved, adjusted to pH 4.0 with acetic acid, and then pressure-filtered with a membrane filter having a pore size of 1 μm to obtain a printability improving liquid 3.

<Preparation of printing property improving liquid 4> Polyallylamine (in-house synthesis: peak position of molecular weight distribution 800 2 parts, styrene-N, N-dimethylaminoethyl methacrylate copolymer (molecular weight 20,000) 1 part, G -50 (benzalkonium chloride: trade name, manufactured by Sanyo Kasei) 1 part, ethylene glycol 5 parts, trimethylolpropane 7 parts, ion-exchanged water 84 parts The above components are mixed and dissolved, and the mixed solution is adjusted to pH 4.0 with acetic acid.
After further adjusting to, further stirring, pressure filtration with a membrane filter having a pore size of 1 μm, and printing property improving liquid 4
Got

Next, using the printability improving liquid and the recording ink set obtained as described above, Canon PP
Recording was performed on C paper (A4 size). The inkjet recording device used at this time was BJF-8500, and the printability improving liquid was discharged using the head and tank for the plain paper water resistance enhancer of the device. In Table 1,
The combinations of the printability improving liquid and the recording ink set used in each Example and Comparative Example are shown below.

[0061]

(Evaluation) The recorded image obtained above was evaluated by the following methods and evaluation criteria. [1. Image Density] A solid image is formed with a printability improving liquid and a black recording ink, and the obtained image is left for 12 hours, and then its reflection density is measured by a reflection densitometer Macbeth RD91.
5 (manufactured by Macbeth) and evaluated by the value. The evaluation criteria are as follows. A: The reflection density is 1.30 or more. ◯: Reflection density is 1.25 or more and less than 1.30. Δ: Reflection density is 1.15 or more and less than 1.25. X: The reflection density is less than 1.15.

[2. Fixability] A red solid image was formed using the printability improving liquid and the recording inks of yellow and magenta, and evaluated by the following methods. After forming a solid image, another blank paper is overlaid on the solid image by its own weight after a certain period of time, and the recorded image is not transferred to the back side of the blank paper until the background stain does not occur. Was measured and the time was used as a measure of fixing property. The measurement time was expressed as time zero at the end of recording. The evaluation criteria using this time are as follows. ◯: Fixability is less than 10 seconds. Δ: Fixability is 10 seconds or more and less than 20 seconds. X: Fixability is 20 seconds or more.

[3. Bleeding] BJF-8500
In the plain paper default mode of No. 3, the printability improving liquid and the recording inks of yellow, magenta, cyan, and black were used to print the solid portions of these four colors adjacently. Then, the degree of bleeding at the boundary between the colors was visually observed and evaluated according to the following criteria. A: Bleeding does not occur at all. ◯: Some bleeding occurs, but there is practically no problem. X: Other than that.

[4. Line Marker Resistance] After printing characters with the printability improving liquid and each of the recording inks of yellow, magenta, cyan and black, one hour has elapsed, the character part is printed with a normal highlighting pressure of a yellow highlighter pen manufactured by Pilot,
It was marked once using a spot writer (trade name).
Then, the marked portion was visually observed and the line marker resistance was evaluated according to the following evaluation criteria. ◯: No bleeding or stains on the white background were found on the printed matter, and the pen tip was not stained. B: No stain on the white background of the printed matter, but the pen tip is slightly stained. X: Soil on the white background is recognized on the printed matter.

[5. Scratch resistance] Four hours after the image is printed with the printability-improving liquid and the recording inks of yellow, magenta, cyan, and black, sillbon paper is placed on the printed paper, and 5 cm on each side. ,
When a weight of 1 kg is placed and the sillbon paper is pulled in this state, it is visually observed whether the non-printed part (white background part) of the recording paper and the sillbon paper are stained by rubbing of the printed part. did. And it evaluated by the following evaluation criteria. ◯: There is no stain on the white background and sillbon paper. Δ: Only sillbon paper has stains. X: There is stain on both the white background and the sillbon paper.

In the above-described embodiment of the present invention, the area where the printability improving liquid adheres to the recording medium is the same area as the image forming area of the recording ink, and the printing duty is the printability improving liquid and the ink. Both are 100%
Is. Table 2 collectively shows the print evaluation results.

[0068]

[0069]

As described above, according to the present invention,
In particular, when color inkjet recording is performed on plain paper, high-speed fixing is realized and high-speed printing is possible, and the obtained image has high image density and bleedlessness, and also has good scratch resistance and Provided are an ink set for inkjet recording, which has high resistance to a marker, and an inkjet printing method.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinichi Tochihara             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Hiroshi Tomioka             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Yutaka Kurabayashi             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2C056 EA05 EE18 FC02 HA44                 2H086 BA01 BA53 BA55 BA59 BA60                 4J039 AB02 AD02 AD03 AD06 AD10                       AD11 AD12 AD13 AD14 AD23                       AE13 BE01 BE22 CA06 EA15                       EA16 EA17 EA19 EA34 EA35                       EA36 EA38 EA42 EA43 EA46                       EA47 GA24

Claims (14)

[Claims] 1. A recording ink containing at least a colorant as an ultrafine particle pigment having a volume average particle diameter of 60 nm or less, and a printability improving liquid for improving printability in an inkjet printer. Inkjet recording ink set. 2. The ultrafine particle pigment used as a colorant has a volume average particle diameter of 60 nm or less and a cumulative 90% particle diameter of the volume particle diameter distribution of 100 nm or less.
Ink set described in. 3. The ink set according to claim 1, wherein the ultrafine particle pigment is a chromatic organic pigment. 4. The ink set according to claim 1, which reacts when the recording ink and the printability improving liquid contact each other. 5. The ink set according to claim 1, wherein the ultrafine particle pigment is a chromatic organic pigment having a functional group dispersible in an aqueous medium on the surface thereof. 6. The functional group dispersible in the aqueous medium,
The ink set according to claim 5, which is an anionic group. 7. The ink set according to claim 1, wherein the ultrafine particle pigment is a chromatic organic pigment dispersed by a dispersant. 8. The ink set according to claim 7, wherein the dispersant is an anionic dispersant. 9. The ink set according to claim 6, wherein the printability improving liquid contains at least a cationic compound. 10. The ink set according to claim 6, wherein the printability improving liquid contains at least a polyvalent metal salt. 11. The ink set according to claim 1, wherein the printability improving liquid contains at least a water-soluble resin component. 12. The printability improving liquid contains a resin component having at least a hydrophilic portion and a hydrophobic portion which are dispersed or dissolved in an aqueous medium.
The ink set according to item. 13. The recording ink comprises a combination of at least four inks of black, cyan, magenta, and yellow, and among these inks, a chromatic ink contains at least an ultrafine particle pigment as a colorant. The ink set according to any one of claims 1 to 12, which comprises. 14. A method for forming a colored portion on a recording medium using the ink set according to claim 1, comprising: (i) applying the recording ink to the recording medium. (Ii) A step of applying the printability improving liquid to the recording medium, wherein the recording ink and the printability improving liquid are applied so as to be in liquid contact with each other on the surface of the recording medium. And a method for printing a colored portion on a recording medium.